Currently, wrenches are widely used to fabricate and maintain machines by screwing or unscrewing each screw element, such as screw nuts, of the machines or components. However, in some highly precise machines, the unscrewing of each screw element requires a specific procedure and an appropriate operation angle. If a careless mistake is made in a manual operation, the screw element or a screw thread in a screw hole may be damaged, or the function and the precision of the machine are impaired.
For the aforementioned reason, some factories provide wrenches having functions of immediately detecting and displaying an angle value. Therefore, when a user exerts force to operate the wrench, the user can immediately know the real angle value of the force. However, the wrench built-in with the functions of immediately detecting and displaying the angle value limits the use and the operation, and is helpless for the user having an old type wrench unless the user additionally buys the aforementioned new type wrench. But, it increases the cost to buy a new wrench, and it is inconvenient for the user who gets used to use a specific wrench or a wrench without being built-in with an angle-detecting function.